This invention relates to a method of and apparatus to remove a protruded, extruded or herniated disc or to decompress a spinal nerve route from lateralstenosis.
U.S. Pat. No. 4,573,448 discloses a method of decompressing herniated discs in the lumbar spine, which can be carried out percutaneously by the insertion of a trocar and cannula over a guidewire extending through the patient""s back towards the herniated disc at an angle of approximately 35 degrees with respect to the patient""s perpendicular line. A hollow cutting instrument is inserted through the cannula to form a window in the disc. Disc fragments are removed through the cannula by means of a forceps instrument. It is disclosed that, as the disc is decompressed, the herniation recedes. It is also stated that, in some cases, it is possible to position the instruments so that the cutting instrument enters the bulge of herniation. As the patent explains, it is a virtue of its postero-lateral endoscopic access that the need for bone removal is avoided, and with it the likely resulting complications.
The patent explains that patients treated in accordance with this new procedure are generally able to ambulate and to sit on the day of surgery, or one day afterwards, that post-operative back pain was minimal and that hospitalisation time is typically as little as two days.
However, the patent also explains that there is a risk of re-herniation through the entry window of the cutting instrument into the disc. As is pointed out in the patent, however, the location of this fenestration, produced by the operation, is such that any re-herniation which does occur is much less likely to apply pressure to the patient""s nerve roots than the original herniation treated by the operative procedure.
It is one aim of the present invention to achieve the benefits of the postero-lateral endoscopic access described in the above US patent, yet at the same time mitigating the disadvantages arising from an operatively produced annulus fenestration in the herniated disc.
According to one aspect of the present invention there is provided a method of treating a herniated spinal disc or to decompress a spinal nerve root encroached by stenosis, including the steps of:
1. removing bone, capsule and capsular ligaments from a co-operating pair of superior and inferior articulating processes (also called facet joints) of the spine to create a path for postero-lateral endoscopic access to the vertebral foramen and to the epidural space of the spinal canal;
2. successively advancing tools of an increasing diameter along said path;
3. advancing through a working cannula of an endoscope in order to visualise the herniated disc material and to check for the presence of nerve roots or dural sac; and
4. engaging soft tissue with a tool in the working cannula, said soft tissue deriving from said herniated disc, and withdrawing said tissue through the cannula, hereby to relieve pressure on nerve structures within the vertebral foramen and spinal canal.
It will be appreciated that, with the method of the present invention, there is no operative invasion of the intact annulus fibrosis of the disc. It is the removal of bone from the articulating process, or facet joint, of the spine, adjacent to the herniated disc, which allows removal of the herniation without penetration into the intact annulus of the disc itself. This bone removal is tolerable because adverse consequences for the patient are significantly less than with the prior art disc-penetrative methods.
In this context, it should be observed that surgical removal of a disc herniation, from within the vertebral canal, using a fully posterior approach, has previously been proposed. However, it is a disadvantage with such a procedure that the nerve structures within the foramen have to be displaced to one side in order to give access to the herniation, and this lateral displacement can be damaging and often creates scar tissue. The presence of this scar tissue usually has adverse consequences and, for this reason, a fully posterior approach is not the method of choice.
In another aspect of the present invention, there is provided apparatus for treating a herniated disc, the apparatus comprising an endoscopic soft tissue removal tool and a working cannula through which said tool can be advanced, the apparatus being characterised by:
means for removing bone from a co-operating pair of superior and inferior articulating processes of the spine, to create a path for postero-lateral endoscopic access to the vertebral foramen and vertebral canal.
In one preferred embodiment, the bone removal means comprises a set of trocar rods of progressively increasing outside diameter, and a corresponding set of hole saw tools, each of which fits snugly over the outside diameter of its corresponding trocar tube and is rotatable on the tube in order to bore through the bony material around the facet joint of the spine corresponding to the herniated spinal disc under treatment.
In one preferred embodiment, the set of hole saw tools has a smallest member with an outside diameter of 5.5 mm and a largest member with an outside diameter of 8.5 mm, with the intervening sizes of hole saws having outside diameters of 6.5 and 7.5 mm, there being four saws in the set. Each of the tools is made of material with a wall thickness of 0.7 mm, so that the corresponding inside diameters of the four saw tools also differ by a 1.0 mm step, from 4.1 mm for the smallest diameter, to 7.1 mm for the largest diameter tool. The four corresponding trocar tools have outside diameters of 4, 5, 6 and 7 mm respectively. The final working cannulas have an outside diameter of respectively 6.5, 7.5 and 8.5 mm.